Monitoring Reaction Intermediates in Plasma-Driven SO, NO, and NO Remediation Chemistry Using In Situ SERS Spectroscopy.

In situ surface-enhanced Raman scattering (SERS) spectroscopy is used to identify the key reaction intermediates during the plasma-based removal of NO and SO under dry and wet conditions on Ag nanoparticles. Density functional theory (DFT) calculations are used to confirm the experimental observations by calculating the vibrational modes of the surface-bound intermediate species. Here, we provide spectroscopic evidence that the wet plasma increases the SO and the NO removal through the formation of highly reactive OH radicals, driving the reactions to HSO and HNO, respectively. We observed the formation of SO and SO species in the SO wet-plasma-driven remediation, while in the dry plasma, we only identified SO adsorbed on the Ag surface. During the removal of NO in the dry and wet plasma, both NO and NO species were observed on the Ag surface; however, the concentration of NO species was enhanced under wet-plasma conditions. By closing the loop between the experimental and DFT-calculated spectra, we identified not only the adsorbed species associated with each peak in the SERS spectra but also their orientation and adsorption site, providing a detailed atomistic picture of the chemical reaction pathway and surface interaction chemistry.